The usual golf ball manufacturing techniques include several different steps, depending on the type of ball, such as one, two, three or even more than three piece balls. According to the traditional method, a solid or composite elastomeric core is made, and an outer dimpled cover is formed around the core.
The two standard methods for molding a cover over a core or a core and inner layers are compression molding and injection molding. The compression molding operation is accomplished by using a pair of hemispherical mold cavities, each of which has an array of protrusions machined or otherwise provided in its cavity, and those protrusions form the dimple pattern on the periphery of the golf ball during the cover molding operation. A pair of hemispherical cover blanks are placed in a diametrically opposed position on the golf ball body, and the body with the cover blanks thereon is placed in the hemispherical molds, and then subjected to a compression molding operation. The combination of heat and pressure applied during the molding operation results in the cover blanks being fused to the golf ball body and to each other to form a unitary one-piece cover structure which encapsulates the golf ball body. In addition, the cover blanks are simultaneously molded into conformity with the interior configuration of the hemispherical molds which results in the formation of the dimple pattern on the periphery of the golf ball cover. When dimple projections are machined in the mold cavity they are typically positioned below the theoretical parting line of the resulting mold cavity. The parting line is typically machined after the dimple forming process. For ease of manufacturing, the parting line on the cavity is usually machined flat normal to the bottom of the inner spherical mold surface. This provides positive shut off preventing flowing cover material from leaking out of the mold. This dimple positioning and flat parting line results in a great circle path on the ball that is essentially void of dimples. This is commonly referred to as the equator, parting line, or seam of the ball. Over the years dimple patterns have been developed to compensate for cosmetics and/or flight performance issues due to the presence of the seam.
As in all molding operations, when the golf ball is removed from the hemispherical molds subsequent to the molding operation, it will have molding flash, and possibly other projecting surface imperfections thereon. The molding flash will be located at the parting line of the hemispherical molds. The molding flash will therefore be on the “equator” of the golf ball.
The molding flash and possible other imperfections projecting from the surface need to be removed and this is normally accomplished by one or a combination of the following: cutting blades, sanding belts, or grinding stones, and the like. These types of processes tend to enhance the obviousness of the seam. Alternative finishing processes have been developed to minimize this effect. These processes include tumbling with abrasive media, stiff brushes, cryogenic de-flashing and the like. Regardless of the finishing process, the result is a flat parting line substantially void of dimple coverage.
When flash is removed by a post-molding operation such as grinding, it is desirable that the molding operation be accomplished in such a manner that the molding flash is located solely on the “land” (undimpled) surface of the golf ball and does not extend into any of the dimples. In other words, the mold flash or other protrusions do not intersect or lie within a dimple boundary. Therefore, prior art hemispherical molds are primarily fabricated so that the dimple-forming protrusions formed therein are set back from the circular rims, or mouths of the cavities.
It is well known that the dimple pattern of a golf ball is a critical factor insofar as the flight characteristics of the ball are concerned. The dimples influence the lift and drag forces exerted on the golf ball which ultimately dictate its overall performance and flight stability. When a golf ball is struck properly, it will spin about an axis and the interaction between the dimples and the oncoming air stream will produce the desired lift, drag, and flight characteristics.
In order for a golf ball to achieve optimum flight consistency, it is beneficial for its dimples to be arranged with multiple axes of symmetry. Otherwise, it might fly differently depending upon orientation. Most prior art golf balls include a single dimple free equatorial parting line, which inherently limits the number of symmetry axes to one. In order to achieve good flight consistency, it is often necessary to compensate for this limitation by adjusting the positions and/or dimensions and/or shapes of certain dimples. Alternatively, additional symmetry axes can be created by incorporating additional dimple free “false” parting lines. However, this practice increases the amount of un-dimpled surface on the ball, which can result in reduced ball flight distance.
For maximum performance and consistency, it is preferable to use a dimple arrangement that requires no adjustment or addition of false parting lines. Therefore, if it is desirable to eliminate the equatorial parting line, it is best that it be done by including dimples that intersect the equator. Some U.S. patents that seek to place dimples upon the equator of the ball include U.S. Pat. Nos. 6,200,232, 6,123,534 and 5,688,193 to Kasashima et al., 5,840,351 to Inoue et al., and 4,653,758 to Solheim. These patents introduced “stepped” and/or “zig zag” parting lines. While this could potentially improve compliance with the symmetry, they did not sufficiently improve dimple coverage, since the parting lines include straight segments that do not permit tight dimple packing on opposite sides of the equator. A stepped path often results in a greater loss of dimple coverage than a straight path because it discourages interdigitation for a larger number of dimples. U.S. Pat. No. 6,936,208 to Ogg teaches the formulation of a partial or continuous tab created by overlapping of adjacent concave and convex tabs to reduce the dimension of the seam about the ball.
Therefore, a need exists for an improved golf ball, made from a mold that would have a parting line configuration that would minimize dimple damage during flash removal, improve symmetry performance, increase surface coverage, minimize the visual impact of the equator, and create a reduced amount of flash and the effort of removing it.